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Re: [Yade-users] total formulation + modifying friction?

 

Do you confirm Vaclav, so I can I commit?

B.

Bruno Chareyre a écrit :
Corresponding output (after fix). It looks better :

trialFs.norm(): 36.0967 vs. maxFs: 24.6416 Fn: 281.663 ks: 341874 tanFric: 0.0874861
displacementT() before slip: 0.000105585
displacementT() after slip: 7.2078e-05
corrected trialFs: 12.4187 -15.884 -14.1663



Bruno Chareyre a écrit :
(discussion moved to yade-dev)

Dem3DofGeom_SphereSphere.cpp:76 reads :

Vector3r diff=.5*(sqrt(currDistSq)/displacementTMax-1)*(p2-p1);
   setTgPlanePts(p1+diff,p2-diff);

What about this instead :

Vector3r diff=.5*(displacementTMax/sqrt(currDistSq)-1)*(p2-p1);
   setTgPlanePts(p1-diff,p2+diff);

It gives stable results and no effect of friction. :)
Still curious about the previous "weighted average".

Bruno




Bruno Chareyre a écrit :
The reason is still not clear but I think I located the problem. slipToDisplacementTmax is not doing what it should.

Outputing data from inside the if(plasticity) condition of Law2_Dem3DofGeom_FrictPhys_Basic, I find this :


trialFs.norm(): 113037 vs. maxFs: 14.9277 Fn: 170.629 ks: 338110 tanFric: 0.0874861
displacementT() before slip: 0.33432
displacementT() after slip: 0.126106
corrected trialFs: -4.40076 9.24839 10.8599

The force is divided by ~10,000, as it should, but the displacement returned by displacementT is only divided by 3. Actually, trialFs is always orders of magnitude higher than maxFs, even after many iterations in a stable packing. It explains why changing friction gives higher forces immediatly.

I've been looking into relocateContactPoints, could you explain this. What is this equation for? It looks like a weird weighted average :

/Vector3r midPt=(effR1/(effR1+effR2))*(p1+p2); // proportionally to radii, so that angle would be the same/

Cheers.

Bruno




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Bruno Chareyre
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Grenoble INP
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